Suction pressure relieving system for a rotary vane compressor

ABSTRACT

A suction pressure relieving system for a rotary vane gas compressor which automatically establishes a safe startup pressure at the compressor inlet ports whenever the compressor is shut down.

Emited States Patent Carl Bloom Springfield, Mass.

Feb. 19, 1970 Jan. 4, 1972 Worthington Compressor and EngineInternational Division of Worthington Corporation, a division ofWorthington Corporation Holyoke, Mass.

Inventor Appl. No. Filed Patented Assignee SUCTION PRESSURE RELIEVINGSYSTEM FOR A ROTARY VANE COMPRESSOR 9 Claims, 1 Drawing Fig.

US. Cl 417/295, 417/439, 417/540 Int. Cl F04c 29/08, F04b 49/00, F04b39/00 Field of Search 417/295,

4-AIR lNLET [5 6] References Cited UNIT ED STATES PATENTS 2,516,2917/1950 Bartholomew 417/20 2,613,026 10/1952 Banks 417/295 3,168,2362/1965 Lamberton et a1. 417/295 3,186,631 6/1965 Lamberton et a1. 417/443,349,994 10/1967 Bloom 417/295 3,448,916 6/1969 Fraser 417/2953,482,768 12/1969 Cirrincione et al. 417/295 Primary Examiner-Carlton R.Croyle Assistant Examiner-John J. Vrablik AttorneyFishman and Van KirkABSTRACT: A suction pressure relieving system for a rotary vane gascompressor which automatically establishes a safe startup pressure atthe compressor inlet ports whenever the compressor is shut down.

Pmmmm 4:972 3.632.231

INVENTOR. CARL BLOOM M WZ%WM ATTORNEYS SUCTION PRESSURE RELIEVING SYSTEMFOR A ROTARY VANE COMPRESSOR BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to the field of rotary vane gascompressors which have throttling valves in the compressor inletconduits for controlling the suction pressure at the compressor inletports. Accordi g y. the general objects of the present invention are toprovide novel and improved apparatus of such character.

2. Background of the Invention In rotary vane compressors where athrottling valve is used to control the compressor output as a functionof the output pressure or load, it is frequently desirable to stop thecompressor to reduce wear and power consumption whenever the demand orload on the compressor is zero for extended periods of time. In suchsituations, highpressure air in the compressor discharge system willleak back past the motionless vanes of the compressor into a confinedportion of the inlet conduit. It is most probable that the suctionpressure control valve in the compressor inlet will have been closedprior to compressor shutdown since it is the no load condition whichcauses the shutdown. In addition, the throttling valves used in suchcompressors often perform both the throttling function and a reverseflow checking function to prevent filters in the inlet line from beingbackwashed and to prevent large quantities of oil laden air from beingexpelled through the air inlet. As a consequence, when the compressor isshutdown, the compressed air which leaks back past the vanes will becaptured within the throttled suction chamber and the compressor inlet.

Rotary vane compressors are designed with a specific compression ratio.It is quite possible that the compressor could be severely damaged if anattempt is made to start the compressor and further compress anabnormally highpressure gas existing at the compressor inlet ports. Thishighpressure condition can arise shortly after shutdown in compressorswhich have the suction pressure throttling valves due to the leakagepast the motionless vanes. The pressure of this highpressure gas at theinlet ports would preclude restarting the compressor if a load demandoccurs shortly after shutdown. It is therefore important that thepressure at the compressor inlet ports be relieved or bled down at leastto a preselected maximum pressure which can be accommodated by thecompressor. This maximum pressure will vary from one rotary compressorto another and will be defined as the maximum compressorstarting inletpressurev It is also desirable that the static shutdown pressure whichexists at both the inlet and discharge sides of the compressor after thehighpressure gas has bled down to an equilibrium condition be as smallas possible to minimize the initial driving torque required to start thecompressor after shutdown.

It is important that the bleeding down of the highpressure gas throughthe compressor not occur too rapidly; otherwise, air dissolved in theoil on the highpressure side of the compressor will create excessivefoam and flood the tanks and filters in the compressor discharge.

In order to reestablish the maximum discharge pressure as soon aspossible after the compressor has been started up, it is desirable tominimize the volume of the discharge system which does bleed through thecompressor into the inlet. This minimization also aids in minimizing thestatic shutdown pressure which will exist across the compressor in theequilibrium condition.

SUMMARY OF THE INVENTION The rotary vane gas compressor of thisinvention has an improved inlet system which provides a pressure at theinlet ports after the compressor has been shutdown which is no greaterthan the preselected maximum compressorstarting inlet pressure toleratedby the particular compressor in question.

The compressor is controlled in its output by means of a conventionalsuction control valve which is located in the compressor inlet conduitto restrict the amount of gas which reaches the compressor while it isrunning. This control valve is operated in response to the compressorload or discharge pressure in the receiver for the highpressure gas.Since the conventional suction control valve is both a throttling valveand a check valve, this valve will in all circumstances be closed whenthe highpressure gases leak back into the inlet suction chamber aftershutdown.

In order to prevent the static shutdown pressure across the compressorfrom exceeding the preselected maximum, an auxiliary tank is connectedinto the suction chamber between the suction control valve and theactual compressor inlet ports.

In order to minimize the volume of highpressure gas which must bediffused into the suction chamber and auxiliary tank, a check valve isinterposed in the compressor discharge manifold at a position close tothe discharge port from the compressor itself. This check valve not onlyserves to minimize the volume of gas to be expanded but in additionmaintains the oil tanks and demister tanks downstream of the compressordischarge manifold under the highpressure after shutdown. Maintainingthese tanks at highpressure prevents oil foaming due to entrapped airand reduces the time necessary to reestablish maximum rated pressureoutput at the discharge ports after a new load demand occurs.

The compressor discharge system includes an oil tank from whichlubricating fluid is fed back to the rotary compressor for lubrication.In order to prevent the oil from being forced under the highpressure inthe discharge system into the rotary compressor, a flow control valve isprovided in the filtered oil feed line to regulate the oil flow andprevent compressor flooding during shutdown.

Since the rate at which the highpressure gas will bleed back into thesuction chamber is dependent upon other compressor design factors andtherefore not readily controllable, a regulated pressure bleedingconduit which bypasses the compressor itself interconnects thehighpressure discharge manifold with the inlet manifold. A valveinterposed in this bleed con duit can be shut off during compressoroperation and regulated during compressor shutdown for the mostdesirable bleed down rate in view of the oilfoaming problem within thecompressor and discharge manifold itself.

If desired, a pressure switch interlocking with the compressor startupsystem may be employed to prevent inadvertent starting when for anyreason the pressure at the inlet ports is not below the maximumcompressorstarting inlet pressure.

BRIEF DESCRIPTION OF THE DRAWING The drawing shows my sucn'on pressurerelieving system which provides a safe compressor starting inletpressure for a rotary vane compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference to the drawing showsthe inlet pressure control system including my improved inlet forrelieving the compressor starting inlet pressure.

The rotary vane compressor is generally designated by the numeral 10.The compressor 10 has an inlet 12 and a discharge manifold 14 whichleads to a discharge receiver 16. The receiver performs the function ofstoring the high-pressure air until it is needed for operating an airhammer or other pneumatic device.

Inlet air which is to be processed by the compressor enters the airinlet 12 and first passes through a filter 18. After the air has beenfiltered it passes to a suction control system which includes a suctioncontrol valve 20 and a suction chamber 22 connected to the rotarycompressor adjacent the inlet ports.

The control valve 20 is a conventional suction control valve whichincludes a springbiased, diaphragmoperated valve stem 24 and a valveplate 26 slidably mounted on the stem 24.

Such valves are well known in the art. The function of such a valve isto regulate the quantity of air which passes to the compressor as afunction of the load or discharge pressure from the receiver 16. Inorder to provide the appropriate pressure control signal for operatingthe valve 20, a control pressure conduit 28 is connected from thedischarge receiver 16 to the valve 20 below diaphragm 29 to control theposition of the springbiased valve stem 24. A pressure regular 27 isincluded in the conduit 28 to adjust the pressure which operates thevalve 20.

Connected to the suction chamber 22 by means of conduit 30 is anauxiliary tank 32 which performs one of the principal functions of myinvention. The tank 32 connects directly into the suction chamber 22 andis carefully matched with the volume of the chamber 22 and thecompressor system to operate as described below.

A pressure sensing switch 34 is also connected to the suction chamber22. The pressure switch may be interconnected with a compressorstartingsystem such as a motor starter which starts the driving motor for thecompressor. The pressure switch 34 is sensitive to the inlet or suctionchamber pressure and prevents starting of the compressor unless theinlet pressure is below the maximum permitted compressorstarting inletpressure. The pressure switch therefore is a safety device supplementingmy improved inlet pressure relieving system.

Highpressure air leaving the compressor 10 through discharge manifold 14first passes through a check valve 36 which prevents reverse flow of thecompressed air in a large portion of the discharge system. Thecompressed air then passes into an oil tank 38 where the bulk of thelubricating oil carried by the highpressure air is deposited. From theoil tank the high-pressure air is transmitted to a demister tank 42where the remaining oil is separated from the air. From the demistertank 42 the oilfree air is transmitted through a second check valve 44to the discharge receiver 16 for use as needed. Check valve 44 maintainspressure in receiver 16 during compressor shutdown The lubricatingsystem for the compressor 10 includes the oil tank 38, the oil filter40, the oil feed line 46, and the oil flow valve 48. The compressed airin the oil tank 38 will force oil through the filter 40 into conduit 46and the compressor 10. Valve 48 is adjusted to control the rate of oilflow to the compressor 10 as needed for its efficient operation and cutsoff flow at shutdown to prevent the oil from flooding the compressor.

In one embodiment of my invention I include a gas pressure bleed line 50connected to the discharge manifold 14 and the suction chamber 22. Ableed valve 52 incorporated in the line 50 is used to adjust the rate atwhich highpressure gas is permittedto flow back into the suction chamber22 after the compressor 10 has been shutdown. Since the rate at whichhighpressure air bleeds through the compressor depends on clearancesestablished for efficient gas compression and, therefore, cannot beindependently designed into the compressor, the bleed line 50 offers aconvenient alternative. During normal compressor operation the valve 52would be closed so that no flow in line 50 will interfere with theregulation of suction chamber pressure by control valve 20.

It is an important feature of my invention that the inlet control systemrelieve the suction chamber pressure when the compressor is shutdown atthe noload condition. The inlet system is designed to reduce the inletpressure to a prescribed value and at a rage which prevents foaming ofthe oil entrained in the highpressure air.

When the rotation of the compressor vanes is stopped, highpressure airwill exist in the compressor itself as well as in the portion of thedischarge manifold 14 between the compressor 10 and check valve 36.Since there is a pressure differential across the compressor 10immediately after shutdown, the highpressure air will tend to leakaround the vanes and rotor of the compressor into the suction chamber22. A controlled leakage rate may be established through bleed line 50with valve 52. The leakage will be prevented from backflowing throughthe filter l8 and air inlet 12 by means of the suction control valve 20.Valve 20 will most likely have been closed due to the noload conditionimmediately prior to compressor shutdown and even if the valve has notbeen closed by the load condition, the flowchecking function of valve 20will prevent undesired backwashing of filter l8 and expulsion of the oilladen air at the inlet 12.

Without the improved inlet system, the equilibrium pressure or staticshutdown pressure generated by the bleed back of highpressure gas couldprevent compressor startup until leakage through the compressor sealsand the suction valve eventually drops the inlet pressure to anacceptable level. This delay in restarting the compressor may severelyhamper its utility particularly where a new demand from the receiver 16arises shortly after the compressor is shut down.

To prevent an undesirably long delay in restarting the compressor, theauxiliary tank 32 is calibrated with the suction chamber 22, compressor10 and manifold 14 to increase the total confined gas volume to a valuewhich will expand the highpressure air in the discharge manifold 14 downto the tolerable maximum compressorstarting inlet pressure, for example,lO p.s.i.g. The tolerable pressure will vary from one compressor toanother depending on its capacity to withstand high discharge pressures.

In order to further reduce the task of expansion performed by theauxiliary tank 32, the check valve 36 is located in the dischargemanifold 14 at a position which will minimize the initial volume ofhighpressure gas which must be expanded into the suction chamber 22 andan auxiliary tank 32. The check valve 36 additionally maintains the oiltank 38 and the remainder of the discharge system under the highpressure. Two advantages are readily apparent. First, lubricating oil intank 38, line 46 and the remainder of the discharge system will not foamdue to entrained air as the discharge manifold 14 is bled down. Second,the total volume of the discharge system which must be pumped up todischarge pressure when the compressor is restarted is minimized andconsequently the time necessary for the compressor 10 to reestablish itsrated discharge pressure is minimized.

The rate at which the small volume of air in discharge manifold 14 isbrought to equilibrium across the compressor 10 can be readilycontrolled by the adjustment of bypass line 52. The controlled rate isdesirable to prevent sudden equalization of the pressures across thecompressor and the resulting foaming of oilladen air in dischargemanifold 14.

It will be understood that the precise system disclosed can have manyforms without departing from the scope of the invention. For example, aspointed out above, the control bleed line 50 is not essential to thesystem. In addition, more than one auxiliary tank 32 may be connected tothe line 30 so that the total volume of the suction chamber 22 and thetanks 32 will establish the desired static shutdown pressure. in thisrespect, however, it should be noted that the added, calibrated volumesof the auxiliary tank 32 will reduce the suction pressure response atthe inlet ports of the compressor 10 to the regulation of suctioncontrol valve 20. It is therefore preferred that the total volume of theauxiliary tanks 32 be calibrated in conjunction with the suction chamber22 to perform the inlet pressure relieving function withoutsignificantly interfering with the throttling function of the suctioncontrol valve 20.

What is claimed is:

1. In a rotary vane gas compressor system including an inlet suctioncontrol valve, a rotary vane compressor having inlet and dischargemanifolds, and a compressed gas receiver, the improvements comprising:

valve means interposed between the compressed gas receiver and thecompressor discharge manifold for preventing flow of compressed gas inthe receiver back into the rotary compressor; and

auxiliary chamber means connected to the rotary compressor inletmanifold and having a preselected minimum volume for reducing the staticshutdown pressure across the rotary compressor to a value not greaterthan a maximum startup inlet pressure limit.

2. The improvements of claim 1 further including:

a oil demister tank connected to the compressed gas receiver upstream inthe direction of normal gas flow from the receiver and downstream withrespect to the valve means.

3. The improvements of claim 1 further including:

an oil reservoir interposed between the valve means and the compressedgas receiver;

an oil feed conduit connecting the oil reservoir with the rotarycompressor; and

an oil flow regulating valve interposed in the oil feed conduit forregulating the flow of oil from the reservoir to the rotary compressor.

4. The improvements of claim 3 still further including:

an oil filter located in the oil feed conduit between the reservoir andthe oil flow regulating valve.

5. An automatic inlet pressure relieving apparatus for a retarypneumatic compressor, said compressor having an inlet, a dischargemanifold and a highpressure gas discharge conduit connecting saiddischarge manifold to a highpressure gas 2 receiver, saidpressurerelieving apparatus comprising:

suction control throttle valve means connected upstream of the gas inletof the rotary compressor;

check valve means connected in the highpressure gas discharge conduitbetween the highpressure gas receiver 25 and the compressor dischargemanifold for checking flow from the receiver back to the compressor; and

an auxiliary suction pressure tank connected to the gas inlet downstreamof the throttle valve means in the direction of gas flow through thethrottle valve, the tank having an internal gas volume contiguous withthe internal volumes of the throttle valve means, the gas inlet, therotary compressor and the gas discharge path between the compressor andcheck valve means, said tank providing a static shutdown pressure at thegas inlet no greater than a preselected maximum pressure.

6. The pressure-relieving apparatus of claim 5 further including:

a pressurebleeding conduit connected at one end to the highpressure gasdischarge between the rotary compres- 40 sor and the check valve meansand at the opposite end to the gas inlet of the compressor; and v ashutoff valve positioned in the pressurebleeding conduit between theends of the conduit whereby the bleeding of the higher pressuredischarge gas through the conduit to the compressor inlet can beshutoff.

7. A suction control inlet for a rotary air compressor having an inletand discharge manifold means including a valve for inhibiting reversedflow of the compressed air comprising:

an inlet conduit defining a passage for admitting a flow of ambient air;

inlet check valve means located in the inlet conduit and oriented totransmit the airflow toward the rotary compressor and prevent reverseflow through the inlet conduit;

suction control means connected with the check valve means andresponsive to the load on the compressor for regulating the inlet airpressure at the rotary compressor; auxiliary chamber means operativelyconnected between the suction control means and the rotary compressor,the chamber means having a chamber volume commensurate with theremaining air volume between the inlet check valve means and the flowinhibiting valve in the discharge manifold means whereby the volume ofcompressed air in the compressor and discharge manifold at shutdown willbe expanded into the auxiliary chamber means volume and remaining volumeat a pressure no greater then a prescribed maximum compressorstartinginlet pressure. 8. The apparatus of claim 7 further including: an airfilter positioned in the inlet conduit at a location upstream in thedirection of inlet airflow from the inlet check valve means whereby thecheck valve means prevents back washing of the air filter.

9. The a paratus of claim 7 wherein: the auxi iary chamber meansincludes at least one tank connected to the compressor inlet downstreamof the suction control means and having an internal volume calibratedfor expansion of the volume of compressed air below the maximumcompressorstarting inlet pressure.

1. In a rotary vane gas compressor system including an inlet suctioncontrol valve, a rotary vane compressor having inlet and dischargemanifolds, and a compressed gas receiver, the improvements comprising:valve means interposed between the compressed gas receiver and thecompressor discharge manifold for preventing flow of compressed gas inthe receiver back into the rotary compressor; and auxiliary chambermeans connected to the rotary compressor inlet manifold and having apreselected minimum volume for reducing the static shutdown pressureacross the rotary compressor to a value not greater than a maximumstartup inlet pressure limit.
 2. The improvements of claim 1 furtherincluding: a oil demister tank connected to the compressed gas receiverupstream in the direction of normal gas flow from the receiver anddownstream with respect to the valve means.
 3. The improvements of claim1 further including: an oil reservoir interposed between the valve meansand the compressed gas receiver; an oil feed conduit connecting the oilreservoir with the rotary compressor; and an oil flow regulating valveinterposed in the oil feed conduit for regulating the flow of oil fromthe reservoir to the rotary compressor.
 4. The improvements of claim 3still further including: an oil filter located in the oil feed conduitbetween the reservoir and the oil flow regulating valve.
 5. An automaticinlet pressure relieving apparatus for a rotary pneumatic compressor,said compressor having an inlet, a discharge manifold and ahigh-pressure gas discharge conduit connecting said discharge manifoldto a high-pressure gas receiver, said pressure-relieving apparatuscomprising: suction control throttle valve means connected upstream ofthe gas inlet of the rotary compressor; check valve means connected inthe high-pressure gas discharge conduit between the high-pressure gasreceiver and the compressor discharge manifold for checking flow fromthe receiver back to the compressor; and an auxiliary suction pressuretank connected to the gas inlet downstream of the throttle valve meansin the direction of gas flow through the throttle valve, the tank havingan internal gas volume contiguous with the internal volumes of thethrottle valve means, the gas inlet, the rotary compressor and the gasdischarge path between the compressor and check valve means, said tankproviding a static shutdown pressure at the gas inlet no greater than apreselected maximum pressure.
 6. The pressure-relieving apparatus ofclaim 5 further including: a pressure-bleeding conduit connected at oneend to the high-pressure gas discharge between the rotary compressor andthe check valve means and at the opposite end to the gas inlet of thecompressor; and a shutoff valve positioned in the pressure-bleedingconduit between the ends of the conduit whereby the bleeding of thehigher pressure discharge gas through the conduit to the compressorinlet can be shutoff.
 7. A suction control inlet for a rotary aircompressor having an inlet and discharge manifold means including avalve for inhibiting reversed flow of the compressed air comprising: aninlet conduit defining a passage for admitting a flow of ambient air;inlet check valve means located in the inlet conduit and oriented totransmit the airflow toward the rotary compressor and prEvent reverseflow through the inlet conduit; suction control means connected with thecheck valve means and responsive to the load on the compressor forregulating the inlet air pressure at the rotary compressor; auxiliarychamber means operatively connected between the suction control meansand the rotary compressor, the chamber means having a chamber volumecommensurate with the remaining air volume between the inlet check valvemeans and the flow inhibiting valve in the discharge manifold meanswhereby the volume of compressed air in the compressor and dischargemanifold at shutdown will be expanded into the auxiliary chamber meansvolume and remaining volume at a pressure no greater than a prescribedmaximum compressor-starting inlet pressure.
 8. The apparatus of claim 7further including: an air filter positioned in the inlet conduit at alocation upstream in the direction of inlet air flow from the inletcheck valve means whereby the check valve means prevents back washing ofthe air filter.
 9. The apparatus of claim 7 wherein: the auxiliarychamber means includes at least one tank connected to the compressorinlet downstream of the suction control means and having an internalvolume calibrated for expansion of the volume of compressed air belowthe maximum compressor-starting inlet pressure.